An electronic apparatus, such as a portable computer, is equipped with a centrifugal fan for cooling the CPU. The centrifugal fan is contained in a housing of the electronic apparatus together with other principal constituent elements, such as a printed circuit board and a hard disc drive.
The centrifugal fan includes a flat fan casing and an impeller that rotates inside the fan casing. The fan casing includes an upper wall and a lower wall facing each other interposing the impeller in between, and a peripheral wall surrounding an outer peripheral portion of the impeller. An intake port is provided on at least one of the upper wall and the lower wall. The intake port is open toward the rotation center of the impeller. Further, an outlet port is provided on the peripheral wall. The outlet port faces the outer peripheral portion of the impeller.
When the impeller rotates, the air inside the housing is drawn into the fan casing via the intake port. The drawn air is expelled from the outer peripheral portion of the impeller, and the velocity energy of the air is converted into a pressure energy inside the fan casing. Thereby, the air expelled into the fan casing from the impeller is discharged into the housing via the outlet port at a desired pressure.
According to the conventional centrifugal fan disclosed in Jpn. Pat. Appin. KOKAI Publication No. 2001-99096, a plurality of outlet ports are provided on the peripheral wall of the fan casing. The air expelled into the fan casing from the impeller is discharged radially with respect to the impeller from the outlet ports. As a result, flow of the air in the fan casing becomes smooth, and the amount of outlet of air increases.
In an electronic apparatus, such as a portable computer, that attaches importance to portability, the housing is required to be decreased in thickness and size. With this requirement, space inside the housing is becoming smaller and smaller, and a variety of constituent elements including a printed circuit board are arranged in a condensed state inside the housing.
Accordingly, even if the constituent elements that generate heat inside the housing are tried to be cooled by the air discharged from the outlet port of the fan casing, the outlet port will be practically occupied by other constituent elements that are adjacent to the centrifugal fan. Consequently, the flow of the air discharged from the outlet port will be disturbed thereby, and it will become difficult to secure a sufficient amount of air that travels toward the heat-producing constituent elements.
Further, according to the conventional centrifugal fan, the air is radially discharged into the housing with respect to the impeller. As a result, when a hotspot that locally receives heat of the constituent elements exists directly above or directly below the outlet port crossing the direction in which the air is expelled, for example, it will be difficult to directly blow the air discharged from the outlet port onto the hotspot.
Furthermore, in order to lead the air discharged from the outlet port to the hotspot, a duct needs to be provided outside the fan casing, so as to vary the direction of the wind. Accordingly, space needs to be secured around the fan casing in order to arrange the duct, which inevitably is disadvantageous in decreasing the size of the housing.